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From: DuyHai Doan <doanduyhai@gmail.com>
Date: Tue, 10 Oct 2017 09:13:42 +0200
Message-ID: <CABNXB2Akg+YULRyeYO--B+BX0DEvuE6VMcrEfZU0=LPEpj5YXg@mail.gmail.com>
Subject: Re: Does NTP affects LWT's ballot UUID?
To: user <user@cassandra.apache.org>
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archived-at: Tue, 10 Oct 2017 07:43:04 -0000

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The ballot UUID is obtained using QUORUM agreement between replicas for a
given partition key and we use this TimeUUID ballot as write-time for the
mutation.

The only scenario where I can see a problem is that NTP goes backward in
time on a QUORUM of replicas, which would break the contract of
monotonicity. I don't know how likely this event is ...

On Tue, Oct 10, 2017 at 9:07 AM, Daniel Woo <daniel.y.woo@gmail.com> wrote:

> Hi guys,
>
> The ballot UUID should be monotonically increasing on each coordinator,
> but the UUID in cassandra is version 1 (timestamp based), what happens if
> the NTP service adjusts system clock while a two phase paxos prepare/commit
> is in progress?
>
> --
> Thanks & Regards,
> Daniel
>

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<div dir=3D"ltr">The ballot UUID is obtained using QUORUM agreement between=
 replicas for a given partition key and we use this TimeUUID ballot as writ=
e-time for the mutation.<div><br></div><div>The only scenario where I can s=
ee a problem is that NTP goes backward in time on a QUORUM of replicas, whi=
ch would break the contract of monotonicity. I don&#39;t know how likely th=
is event is ...</div></div><div class=3D"gmail_extra"><br><div class=3D"gma=
il_quote">On Tue, Oct 10, 2017 at 9:07 AM, Daniel Woo <span dir=3D"ltr">&lt=
;<a href=3D"mailto:daniel.y.woo@gmail.com" target=3D"_blank">daniel.y.woo@g=
mail.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" style=
=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir=
=3D"ltr"><div>Hi guys,</div><div><br></div>The ballot UUID should be monoto=
nically increasing on each coordinator, but the UUID in cassandra is versio=
n 1 (timestamp based), what happens if the NTP service adjusts system clock=
 while a two phase paxos prepare/commit is in progress?<span class=3D"HOEnZ=
b"><font color=3D"#888888"><br clear=3D"all"><div><br></div>-- <br><div cla=
ss=3D"m_-535379867790778533gmail_signature" data-smartmail=3D"gmail_signatu=
re">Thanks &amp; Regards,<br>Daniel</div>
</font></span></div>
</blockquote></div><br></div>

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